The present invention generally relates to the management of snapshots.
Technology for managing snapshots is known. Such technology is handled by a file server, and more specifically, by network storage such as a NAS (Network Attached Storage) device, for example. In cases where the technology is handled by a NAS device, the latest state of the file system is maintained by way of file updates or the like while holding static images of the file system at certain time points. Snapshots make it possible to acquire a plurality of generation backups and are disclosed in Japanese Application Laid Open No. 2004-342050, for example.
In the management of the snapshots of a first logical volume, for example, in cases where data elements corresponding to a write target are written to a first logical volume at or after the snapshot acquisition time points, data elements prior to the update resulting from the writing of these data elements are saved to a second logical volume.
In this snapshot management, by overwriting erasure-corresponding data elements which are data elements corresponding to an erasure target and which are stored in the first logical volume at or following the snapshot acquisition time point, for example, with erasure data elements which are data elements signifying erasure (data elements represented by “0”, for example), even in cases where the erasure target is erased from the first logical volume, the erasure-corresponding data elements are saved to the second logical volume. Hence, the erasure-corresponding data elements remain in the second logical volume, and consequently, there is a risk that the corresponding erasure data will be leaked. This is more of a problem in cases where the erasure target is highly confidential information such as personal information.